Reversible mixing impeller

Abstract

Liquid mixing impellers particularly designed for the chemical processing industry provide a generally axial flow when rotated in a first direction of rotation and provide a generally radial flow when rotated in the opposite direction of rotation. The blades are formed of sheet material with an edge which leads in the first direction of rotation being defined by a portion of the blade which is folded and turned in a chordwise sense through a limited extent back upon itself. The folded back leading edge forms a rearwardly facing concavity which faces the blade trailing edge. The power number in the radial flow rotation direction substantially exceeds the power number in the axial flow rotation direction.

What is claimed is: 
     
       1. A liquid mixing impeller operable by changing the direction of rotation to produce distinctively differing mixing modes, comprising: said impeller having a hub for mounting on a driven shaft,   a plurality of substantially identical blades each extending generally radially from said hub, said blades each having a root portion attached to said hub and each having axially remote blade tips,   each of said blades being formed of sheet material having generally radially extending chordwise spaced edges extending from said root portion to said tip,   the same one of said blade edges on each of said blades being defined by a blade portion folded and turned back upon itself through a limited chordwise extent to form a concavity which faces the other blade edge,   the remainder of each of said blades being relatively flat and being inclined with respect to the axis of said hub when viewed from said blade tips to define a positive pitch angle with respect to the plane of rotation of said blades thereby defining for each of said blades a pressure side on one side of said blade and a suction side on the opposite side of said blade such that said concavities are positioned on said blade suction sides when said impeller is rotated in the direction wherein said folded edge portions are the leading edges, and said impeller generates an axial flow and whereby said impeller is rotated in the opposite direction said concavities cause said blades to develop a radially outward flow.   
     
     
       2. The mixing impeller of claim 1 in which said concavities are generally semi-cylindrical when viewed from said blade tips. 
     
     
       3. The mixing impeller of claim 1 in which said blade concavities are semi-elliptical when view from said blade tips. 
     
     
       4. The mixing impeller of claim 1 in which said blade concavities are generally wedge-shaped when viewed from said blade tips. 
     
     
       5. The mixing impeller of claim 1 in which the chordwise extent of said turned back blade portions define a blade thickness and in which the chordwise length of said blades, thereby defining an aspect ratio to said thickness between 2:1 to 4:1. 
     
     
       6. The impeller of claim 1 in which each said blade is formed as half of an ellipse which has been cut at an angle of about 30° to the major axis of the ellipse. 
     
     
       7. The impeller of claim 1 which has a ratio between the power number in said opposite direction of rotation to the power number in said first named direction of rotation of between about 1.3 to 1 to about 1.4 to 1. 
     
     
       8. In a liquid mixing impeller including a hub mounted on a shaft and operated in either of two directions of rotation, and a plurality of blades extending generally radially of said hub, the improvement comprising: each of said blades defining a leading edge and a trailing edge in one said direction of rotation and a body portion extending chordwise between said leading and trailing edges to form a positive pitch angle with respect to a common plane of rotation of said blades,   said blades at adjacent said leading edges each having a chordwise length of material which forms a curved blade portion which extends toward said trailing edge and terminates at a chordwise position which position is a fraction of the chordwise extent of said blade body portion, said curved blade portion defining with said body portion a generally concave radially extending pocket immediately behind said leading edge and facing said trailing edge and defining in said one direction of rotation a blade suction side including said pocket, and a blade pressure side opposite said suction side,   whereby when said impeller is rotated in said one direction it generates an axial flow and when said impeller is rotated in the opposite direct said pockets cause said blades to develop a radially outward flow.   
     
     
       9. A liquid mixing impeller according to claim 8 in which said chordwise lengths of material extend spanwise the radial extent of said blades.